v0.0.38: FC-P4 complete — session versioning, wire envelope, auto-backup

FC-P4-T1: Session State Versioning
- RatchetState serialize/deserialize with [MAGIC:0xFC][VERSION:1][bincode]
- Legacy (raw bincode) still loads — backward compatible
- Client + WASM both use versioned format
- 2 new tests: roundtrip + legacy compat

FC-P4-T2: WireMessage Versioning Envelope
- Format: [WZ magic][version:u8][length:u32 BE][bincode payload]
- Server + client + WASM accept both envelope and legacy on receive
- Client still sends raw bincode (server handles both)
- Future version → "update required" error instead of crash
- 3 new tests: roundtrip, legacy compat, future version rejection

FC-P4-T3: Periodic Auto-Backup
- Every 5 minutes, encrypts sessions+contacts+sender_keys to ~/.warzone/backups/
- HKDF-derived key from seed, ChaCha20-Poly1305 AEAD
- Atomic writes (temp file + rename), rotates to keep last 3
- /backup command for manual trigger

127 tests passing (was 122)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/crates/warzone-client/src/tui/commands.rs

@@ -47,6 +47,7 @@ impl App {
                 "  /info               Show your fingerprint",
                 "  /eth                Show Ethereum address",
                 "  /seed               Show recovery mnemonic (24 words)",
+                "  /backup             Create encrypted backup now",
                 "  /peer <fp>, /p      Set DM peer by fingerprint",
                 "  /peer @alias        Set DM peer by alias",
                 "  /reply, /r          Reply to last DM sender",
@@ -189,6 +190,19 @@ impl App {
             }
             return;
         }
+        if text == "/backup" {
+            if let Ok(seed) = crate::keystore::load_seed_raw() {
+                match db.create_backup(&seed) {
+                    Ok(path) => {
+                        self.add_message(ChatLine { sender: "system".into(), text: format!("Backup saved: {}", path.display()), is_system: true, is_self: false, message_id: None, timestamp: Local::now() });
+                    }
+                    Err(e) => {
+                        self.add_message(ChatLine { sender: "system".into(), text: format!("Backup failed: {}", e), is_system: true, is_self: false, message_id: None, timestamp: Local::now() });
+                    }
+                }
+            }
+            return;
+        }
         if text == "/friend" || text == "/friends" {
             // Fetch encrypted friend list from server, decrypt locally
             let url = format!("{}/v1/friends", client.base_url);